So here's what's going on:
If I use ChickHEN while the CXMB theme folder is on the psp, and it's listed in the VSH, it will freeze when I press the O button to install 5.03 GEN-A, then shut off.
I tried ChickHEN without the CXMB folder and the entry in the VSH. After ChickHEN rebooted the PSP...